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4.3 KiB
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90 lines
4.3 KiB
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<!-- $Id: BPolygonUseCases.html,v 1.1 2002/10/28 02:50:08 jrand Exp $ -->
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<TITLE>BPolygon Use Cases and Implementation Details</TITLE>
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<BODY BGCOLOR="white" LINK="#000067" VLINK="#000067" ALINK="#0000FF">
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<FONT FACE="Verdana,Arial,Helvetica,sans-serif" SIZE="-1">
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<H1>BPolygon Use Cases and Implementation Details:</H1>
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<P>This document describes the BPolygon interface and some basics of how it is implemented.
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The document has the following sections:</P>
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<OL>
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<LI><A HREF="#interface">BPolygon Interface</A></LI>
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<LI><A HREF="#usecases">BPolygon Use Cases</A></LI>
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<LI><A HREF="#implement">BPolygon Implementation</A></LI>
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</OL>
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<A NAME="interface"></A><H2>BPolygon Interface:</H2>
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<P>The BPolygon class is used to hold information about a shape composed of a series of straight
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lines (ie a polygon). On its own, it just describes the shape and can only be drawn by passing
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it to a BView. The best source of source of information for the BPolygon interface can be found
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<A HREF="file:///boot/beos/documentation/Be%20Book/The%20Interface%20Kit/Polygon.html">here in the Be Book</A>.
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</P>
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<A NAME="usecases"></A><H2>BPolygon Use Cases:</H2>
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<P>The following use cases cover the BPolygon functionality:</P>
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<OL>
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<LI><P><B>Construction 1:</B> A BPolygon can be constructed without passing it any arguments. When
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this is done, the polygon will have no points in it (ie no shape) until they are added through
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AddPoints().</P></LI>
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<LI><P><B>Construction 2:</B> A BPolygon can be constructed by passing it a pointer to an existing
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BPolygon (ie a copy constructor). The resulting copy will have the exact same state as the
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one passed in. That means it will have the same number of points in the same locations resulting
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in the same shape.</P></LI>
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<LI><P><B>Construction 3:</B> A BPolygon can be constructed by passing it a pointer to an array of
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BPoints and an integer which describes the number of points in that array. The BPolygon will be
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constructed such that it holds the shape described by that array of points.</P></LI>
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<LI><P><B>Destruction:</B> When a BPolygon is deconstructed any memory allocated in order to hold
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the state of the BPolygon is freed and the state of the polygon is lost.</P></LI>
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<LI><P><B>Add Points:</B> The AddPoints() member function appends a number of passed in points to
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the existing set of points already in the polygon. It takes a pointer to an array of BPoints and
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an integer count of the number of points to append. This is similar to the "Construction 3" use
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case except in that case there is no existing points so the passed in points describe the entire
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polygon.</P></LI>
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<LI><P><B>Count Points:</B> The CountPoints() member function returns the number of points which
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describe the polygon. The result is an integer.</P></LI>
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<LI><P><B>Frame:</B> The Frame() member function returns the smallest BRect which contains all of
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the points which describes the BPolygon.</P></LI>
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<LI><P><B>Map To:</B> The MapTo() member function applies a translation (ie move) and a scale (ie
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grow/shrink) operation to the existing polygon, adjusting all points according to the passed in
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rule. The operation to apply depends on two passed in BRect's. The translation and scale
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adjustment which turns the first BRect into the second BRect is applied to all points in the
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BPolygon.</P></LI>
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<LI><P><B>Print To Stream:</B> The PrintToStream() member function sends the set of points which
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make up the BPolygon to standard output. It does so by performing a PrintToStream() on the
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individual BPoint's which make up the polygon. This member is generally used for debugging and
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the output is primarily human readable and not sensitive to changes which could risk backward
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compatibility.</P></LI>
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<LI><P><B>Assignment Operator</B> The operator=() operator is defined for BPolygon's. It takes
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a source BPolygon and assigns it to another existing BPolygon target. The state of the target
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BPolygon is lost and replaced with that of the source. The source retains its state so the outcome
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is two BPolygons with the same state (ie set of points).</P></LI>
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</OL>
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<A NAME="implement"></A><H2>BPolygon Implementation:</H2>
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<P>Internally, the BPolygon contains an array of BPoint's which it uses to track the shape it
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holds. The implementation of BPolygon is fairly simple since it is a fairly basic container
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class for a set of points.</P>
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